Transfer line heater in calcining fluid coke



1961 .1. w. BROWN ET AL 2,998,354

TRANSFER LINE HEATER IN CALCINING FLUID COKE Filed Feb. 4, 1960 fl-- [we l2 TRANSFER LINE HEATER COKE SOAKERL- AIR 7 6 4 PREIQEXTER BLOWER James W. Brown Harvey E. W. Burnside Inventors Edward A. Destremps By y M7 Patent Attorney 2,998,354 TRANSFER LINE HEATER IN CALCINING FLUID COKE James W. Brown, The Hague, Netherlands, and Harvey E. W. Burnside, Locust, and Edward A. Destrernps, Murray Hill, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Feb. P, 1960, Ser. No. 6,698 11 Claims. (Cl. 202-31) This invention relates to improvements in calcining fluid coke. More particularly it relates to a. process wherein fluid coke is calcined by quickly heating it Whilein the form of a dispersed suspension in a transfer line under carefully controlled combustion conditions followed by soaking the coke in the presence of an inert gas.

There has recently been developed an improved process known as the fluid coking process for the production of fluid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions, e.g., see US. Patent No. 2,881,130, granted April 8, 1959 to Pfeiffer et a1. For completeness the process is described in further detail below although it should be understood that the fluid coking process itself is no part of this invention.

The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. Ina typical operation the heavy oil to be processed is injected into the reaction vessel containing a dense turbulent fluidized bed of hot inert solid particles, preferably coke particles. A transfer line or staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate. A stream of coke is thus transferred from the reactor to the burner vessel, such as a transfer line or fluid bed burner, employing a standpipe and riser system, air being supplied to the riser for conveying the solids to the burner. Suflicient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, is burned for this purpose. This may amount to approximately 15% to 30% of the coke made in the process. The net coke production, which represents the coke make less the coke burned, is withdrawn.

Heavy hydrocarbon oil feeds suit-able for the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically, such feeds can have an initial boiling point of about 700 F. or higher, an A.P.I. gravity of about to 20, and a Conradson carbon residue content of about to 40 Wt. percent. (As to Conradson carbon residue see A.S.T.M. Test D-189-41.)

The method of fluid solids circulation described above ited States atent ice is Well known in the prior art. Solids handling technique is described broadly in Packie Patent No. 2,589,124, issued March 11, 1952.

The fluid coke product particles have a particle diameter predominantly, i.e., about 60 to 90 wt. percent, in the range of 20 to mesh, a sulfur content in many cases above 6 Wt. percent, and a volatile content of 2 to 10 wt. percent. They have a real density of about 1.4 to 1.7 which is too low for use in the manufacture of carbon electrodes in making aluminum and other purposes. Increased density and lower sulfur and volatile content are particularly necessary before the fluid coke is suitable for manufacture into electrodes, one of the potential uses of petroleum coke. These can be accomplished by calcining the coke at high temperatures, e.-g., minimum temperatures of 2100 F. or higher. These temperatures and the times required make the calcining operation relatively dilficult and expensive.

This invention provides an improved process for calcining fluid coke. The process comp-rises quickly heating the fluid coke particles while in the form of a relatively dilute dispersed suspension in a transfer line by the carefully controlled combustion of a gaseous extraneous fuel with an oxygen-containing gas followed by soaking the thus treated coke in the presence of an inert gas. Further details are presented below.

The rate of the oxygen-containing gas utilized in the combustion is important and is adjusted so as to give 10 to 30 Weight percent excess oxygen on coke after complete combustion of the gaseous extraneous fuel. Excess oxygen is defined as the amount of oxygen supplied that is not needed for theoretical complete combustion of all the fuel gas supplied. This is import-ant since smaller quantities of oxygen lead to excessive carbon monoxide and hydrogen formation, whereas larger quantities result in the loss of coke through burning. The high oxygen content of the usually preheated gas, e.g., air, assures rapid combustion of the extraneous fuel so that the coke quickly heats to a temperature of 1800 F. to give off its volatile matter which in turn is burned along with unburned extraneous fuel to further heat the coke to about 2400 F. to 3000 F. Air is the more conveniently utilized oxygen-containing gas.

The solids residence time in the transfer lineheater is maintained in the range of about 0.1 to 3.0 seconds to minimize their combustion and to minimize the reduction of CO to CO.

The gaseous extraneous fuels that can be utilized include natural gas, methane, propane etc. Natural gas is preferred. The amount of extraneous fuel utilized is in the range of about 0.5 to 1.5 s.c.f./lb. of coke, for example, 1.05. This supplies part of the total fuel requirements and the remainder is supplied by evolved volatile material from the fluid coke particles. The natural extraneous gas burns in preference to the coke which minimizes loss of coke by combustion because the oxygen which would be available to burn the coke is used up in burning the natural gas. This allows more air to be used to heat the coke without sufiering large coke losses by combustion.

The heated coke is then soaked in a separate soaking zone at a temperature in the range of about 2400 F. to 3000 F. for a period of time in the range of 0.5 to 3.0 hours so as to further increase the density and provide for the recovery of valuable materials from the coke. The solids move through the soaking zone as a downwardly moving bed which may be fluidized at its top by the upflowing gases evolved fromthe coke during the soakmg.

This invention will be better understood by reference to the flow diagram shown in the drawing.

Referring now to the flow diagram, hot coke from the fluid coke burner at a temperature of about 1000 F.- 1300 F. containing about 7 wt. percent sulfur, enters the bottom portion of a vertically arranged transfer line burner 1 through line 2. While the transfer line burner is shown as vertically arranged it can be inclined or horizontally arranged. Transfer line burner I typically has the following dimensions, e.g., 8 /2 ft. inside diameter and 60 ft. long. The figures presented assume a feed rate of 1050 tons a day of fluid coke. 29,500 s.c.f.m. of air leave blower 3 and enter preheater 5 through line 4. The temperature of the air in passing through preheater 5 is raised to about 500 F. to 1500 F., e.g. 1000 F., and it enters the bottom portion of the transfer line burner through line 6. About 1520 s.c.f.m. of natural gas are fed into the bottom portion of the transfer line burner through line 7. The coke is thus formed into a dispersed suspension and heated at high velocity by the burning gaseous stream, evolved flue gas and other gaseous materials. The temperature of the coke is thus raised to about 2750 F. by the combustion of evolved volatile materials and extraneous natural gas. Its velocity in the transfer line burner is about 60 ft. per second and the solids residence time in this design is about 1 second. The amount of air utilized results in 17.5 wt. percent excess oxygen on coke after complete combustion of the natural gas.

The density of the suspension of coke particles passing up through the transfer line burner 1 is between about 0.25 and 1.30 lb./lb. of gas. Using 1.05 s.c.f. of methane per lb. of coke and 17.5 wt. percent excess oxygen on coke the density of the suspension passing up through the transfer line at the stated velocity of about 60 feet per second is about 0.64 lb./ lb. of gas or about 0.007 lb. coke/ cubic foot of gas under the actual temperature and pressure.

The coke, carbon dioxide and flue gases are then sent into cyclone 8 or other solid vapor separating devices. The flue gases are withdrawn through line 9 while the solids are discharged via line 11 into soaker 10. Line 11 leads to the top of the soaker 10 in which a level of coke solids is maintained, as shown at 10, above the outlet end of line 11 to prevent gaseous efliuent from backing up through the separator 8. Line 11 is inclined from the vertical and leads into the side of the soaker 10 to permit building up the solids level 10' into the soaker as just explained.

The soaker conveniently has the following dimensions, 10 inside diameter x 32 high. The hot coke is kept at a temperature of about 2750" F. for about one hour in soaker 10. The gaseous eflluent withdrawn from the soaker through outlet line 12 which opens into the top of the soaker above the outlet end of line 11 contains about 61 mole percent carbon disulfide, about 24 mole percent hydrogen sulfide and about mole percent sulfur. The pressure in the cyclone is higher than in the soaker. This gaseous eflluent is conveniently sent to a carbon disulfide recovery plant. The product coke is withdrawn through bottom line 13 and contains about 1 /2 wt. percent sulfur. This coke can be cooled by indirect heat exchange in a waste heat boiler, by water quenching or by any other convenient means.

The final temperature of the coke can be controlled by introducing it at several points in the transfer line. Cold coke could be introduced at several locations to avoid quenching the burning reaction at the transfer line inlet which would prevent the release of volatile matter. It is also possible to introduce secondary air at locations downstream from the point of initial air introduction so as to maximize the CO /CO ratio.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illustrate how the fluid coke was prepared.

Conditions in fluid coker reactor Broad Preferred Range Range Temperature, F 850-1, 200 900-1, 000 Pressure, Atmospheres 1-10 1. 5-2 Superficial Velocity of Fluidizing Gas, Ft./sec 0. 2-10 0. 5-4 Feed Rate (Solids/Oil Ratio) 2-30 7-15 In order to summarize the conditions more fully, the following tables are presented.

Conditions in transfer line burner Broad Range Preferred Range Coke Temperature, F 2, 400-3, 000 2, (300-2, 800 Pressure, Atmospheres 1-5 1. 5-3.0 Outlet Gas Temperature, F 2, 500-3, 200 2, 800-3, 000 Superficial Velocity of Gas, ft./see-.- 10-100 50-70 Solids Residence Time, Sec 0.1-3.0 0. 4-2. 0 Excess Oxygen, lbs/lb. of coke, wt. percent 10-30 15-25 Conditions in soaker Broad Range Preferred Range Residence Time, Hours 0. 5-3 1-2 Temperature, F 2, 400-3, 000 2, 600-2, 800 Pressure, atmospheres 0. 5-3 1.0-2.0

The advantages of this invention will be apparent to the skilled in the art. The coke loss is held to a low value, e.g., less than about 5% because of the controls on the excess oxygen content and solids residence time. The reduction of CO to CO is kept at a minimum giving high fuel efficiency. Air pollution is reduced because the sulfur is recovered predominantly as carbon disulfide. This results in valuable economies as contrasted to the conversion of sulfur to less value compounds. The evolved volatiles are utilized as fuel in the transfer line heater resulting in fuel economies. The problem of corrosion is reduced since the sulfur release in the transfer line is low and an oxidizing atmosphere can be maintained, permitting silicon carbide brick or magnesia brick to be used without appreciable corrosion. All these advantages are obtained in a simple, economic process.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

This patent application is a continuation-in-part of the Brown et al. patent application, Serial No. 631,840, filed December 31, 1956, now abandoned.

What is claimed is:

1. A process for desulfurizing and increasing the density of fluid coke particles containing a high percentage of sulfur, said fluid coke particles having been produced by contacting a heavy petroleum oil coking charge stock at a coking temperature with a body of fluidized coke particles in a reaction zone wherein the oil is converted to product vapors and carbonaceous material is continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke particles from the coking zone in a heating zone to increase the temperature of said fluidized particles, returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing coke product particles, which comprises the steps of heating the coke particles while in the form of a high velocity dispersed suspension in a transfer line heating zone to a temperature in the range of about 2400 F. to 3000 F. by the combustion initially of an added gaseous extraneous fuel with an oxygen-containing gas, the gaseous fuel being utilized in an amount of about 0.5 to 1.5 s.c.f./lb.

of coke solids and the oxygen-containing gas being utilized in an amount so as to give to 30 wt. percent excess oxygen on coke after combustion of the gaseous extraneous fuel, the coke solids residence time in the transfer line heating zone being in the range of about 0.1 to 3.0 seconds, separating the thus heated coke particles from the resultant flue gas, maintaining the coke particles in a soaking zone at a temperature in the range of about 2400 F. to 3000" F. for a time interval of about 0.5 to 3 hours and the-n withdrawing the desulfurized coke particles from the soaking zone.

2. A process for calcining fluid coke particles containing sulfur, said fluid coke particles having been produced by contacting a heavy petroleum oil coking charge stock at a'coking temperature with a body of fluidized coke particles in a reaction zone wherein the oil is converted to product vapors and carbonaceous material is continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke particles from the coking zone in a heating zone to increase the temperature of said fluidized particles, returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing coke product particles, which comprises the steps of heating the coke particles while in the form of a high velocity dispersed suspension in a transfer line heat ing zone to a temperature of at least about 2400 F. by the combustion initially of an added gaseous extraneous fuel with an oxygen-containing gas, the gaseous fuel being utilized in an amount of about 0.5 to 1.5 s.c.f./lb. of coke solids and the oxygen-containing gas being utilized in an amount so as to give 10 to 30 wt. percent excess oxygen on coke after combustion of the gaseous extraneous fuel, the density of the coke particles in the suspension passing through said transfer line heating zone being between about 0.25 and 1.30 pound per pound of gas, the coke solids residence time in the transfer heating zone being in the range of about 0.1 and 3.0 seconds, separating the thus heated coke particles from the resulting flue gas, maintaining the heated coke particles in a soaking zone at a temperature of at least about 2400 F. for a time interval of about 0.5 and 3 hours and then withdrawing the calcined coke particles from the coking zone.

3. A process for desulfurizing and increasing the density of fluid coke particles containing a high percentage of sulfur, said fluid coke particles having been produced by contacting a heavy petroleum oil coking charge stock at a coking temperature with a body of fluidized coke particles in a reaction zone wherein the oil is converted to product vapors and carbonaceous material is continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke particles from the coking zone in a heating zone'to increase the temperature of said fluidized particles, returning a portion of the heated-coke particles from the heating zone to the coking zone and withdrawing coke product particles, which comprises the steps of heating the coke particles while in the form of a high velocity dispersed suspension in a transfer line heating zone to a temperature of at least about 2400 F. by the combustion initially of an added gaseous extraneous fuel and combustion of volatile material evolved from heating the coke above about 1800 F. with an oxygen-containing gas, the gaseous fuel being utilized in an amount of about 0.5 to 1.5 s.c.f./lb. of coke solids and the oxygencontaining gas being utilized in an amount so as to give 10 to 30 wt. percent excess oxygen on coke after combustion of the gaseous extraneous fuel, the density of the coke particles in suspension passing through said transfer line heating zone being between about 0.25 and 1.30 pound per pound of gas, separating the thus heated coke particles from the resultant flue gas, maintaining the coke particles in a soaking zone at a temperature above about 2400 F. for a time interval above about 0.5 hour and then withdrawing the desulfurized coke particles from the soaking zone.

4. In a process for calcining fluid coke particles containing sulfur, said fluid coke particles having been produced by contacting a heavy petroleum oil coking charge stock at a coking temperature with a body of fluidized coke particles in a reaction zone wherein the oil is converted to product vapors and carbonaceous solids are continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke particles from the coking zone in a heating zone to increase the temperature of said fluidized particles, returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing coke product particles, passing the withdrawn coke particles to a soaking zone maintained at a temperature up to about 3000 F. for a time interval of about 0.5 to 3 hours and then withdrawing the calcined coke particles from said soaking zone, the improvement in the step of heating which comprises rapidly heating the coke particles while in the form of a high velocity dispersed suspension in a vertically arranged heating zone formed as a confined passageway having a substantially uniform diameter to a temperature up to about 3000" F. by the combustion initially of an added gaseous extraneous fuel with an oxygen-containing gas, the gaseous fuel being added directly to said dispersed suspension and utilized in an amount of 0.5 to 1.5 s.c.f./ lb. of coke solids and the oxygen-containing gas being utilized in an amount so as to give 10 to 30 weight percent excess oxygen on coke after combustion of the gaseous extraneous fuel and the coke solids residence time in said vertically arranged heating zone being in the range of 0.1 to 3.0 seconds.

5. In a process for calcining fluid coke particles containing sulfur, said fluid coke particles having been produced by contacting a heavy petroleum oil coking charge stock at a coking temperature with a body of fluidized coke particles in a reaction zone wherein the oil is converted to product vapors and carbonaceous material is continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke particles from the coking zone in a heating zone to increase the temperature of said fluidized particles, returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing coke product particles, passing the withdrawn coke particles to a soaking zone maintained at a temperature up to about 3000 F. for a time interval of about 0.5 to 3 hours and then withdrawing the desulfurized coke particles from said soaking zone, the improvement in the step of heating which comprises rapidly heating the coke particles while in the form of a high velocity dispersed suspension in a transfer line heating zone formed as a confined passageway to a temperature up to about 3000 F. by the combustion initially of an added gaseous extraneous fuel with an oxygen-containing gas, the gaseous fuel being added directly to said dispersed suspension and utilized in an amount of about 0.5 to 1.5 s.c.f./lb. of coke solids and the oxygen-containing gas being utilized in an amount so as to give 10 to 30 weight percent excess oxygen on coke after combustion of the gaseous extraneous fuel and the coke solids residence time in said transfer line heating zone being in the range of about 0.1 to 3.0 seconds.

6. A process according to claim 4 wherein the excess oxygen-containing gas is in the range of about 15 to 25 wt. percent based on coke.

7. A process according to claim 4 wherein said dis persed suspension in said heating zone has a density less than about 1.30 lb. of coke per pound of gas.

8. The process of claim 1 in which the oxygen-containing gas is preheated to a temperature in the range of about 500 to 1500 F.

9. The process of claim 2 in which the excess oxygen is in the range of 15 to 25 wt. percent.

10. An apparatus of the character described including i a vertically arranged elongated high velocity transfer line heating vessel, an inlet for solid particles into the bottom end of said heating vessel, a second inlet adjacent said first inlet for introducing gasiform material into the bottom end of said transfer line, a solids-gasiform separating means on the outlet end of said transfer line heating vessel for separating solids from gasiform material, a solids receiving vessel, a downwardly directed pipe leading from the bottom portion of said separating means through a side wall to an intermediate portion of said solids separating means for conducting solids from said separating means to said solids receiving vessel and adapted to maintain a column of solids therein to form sealing means between said separating means and said solids receiving vessel for preventing backflow of gases from said solids receiving vessel, a line leading from the top of said solids receiving vessel above the outlet end of said downwardly directed pipe for removing gasiform material from the upper portion of said solids receiving vessel and an outlet line leading from the bottom portion of said solids receiving vessel for removing solids from said solids receiving vessel.

11. An apparatus of the character described including an elongated transfer line high velocity heating vessel, an inlet for solid particles into one end of said heating vessel, a second inlet adjacent said first inlet for introducing gasiform material into the same end of said transfer line, a solids-gasiform separating means on the outlet end of said transfer line heating vessel for separating solids from gasiform material, a solids receiving vessel, a downwardly directed pipe leading from the bottom portion of said separating means and leading to the upper portion of said solids receiving vessel below the top thereof and through the side wall at one side thereof to conduct solids from said separating means to said solids receiving means to form sealing means between said separating means and said solids receiving vessel for preventing backfiow of gases from said solids receiving vessel to said separating means, an outlet line leading from the top of said solids receiving vessel and arranged above the outlet end of said downwardly directed pipe for removing gasiform material from the top of said solids receiving vessel and an outlet line leading from the bottom portion of said solids receiving vessel for removing solids from said solids receiving vessel.

References Cited in the file of this patent UNITED STATES PATENTS 2,734,853 Smith et al. Feb. 14, 1956 2,735,804 Boston et a1. Feb. 21, 1956 2,743,216 Jahnig et al. Apr. 24, 1956 2,743,218 Herrmann Apr. 24, 1956 2,789,085 Rollman Apr. 16, 1957 

1. A PROCESS FOR DESULFURIZING AND INCREASING THE DENSITY OF FLUID COKE PARTICLES CONTAINING A HIGH PERCENTAGE OF SULFUR, SAID FLUID COKE PARTICLES HAVING BEEN PRODUCED BY CONTACTING A HEAVY PETROLEUM OIL COKING CHARGE STOCK AT A COKING TEMPERATURE WITH A BODY OF FLUIDIZED COKE PARTICLES IN A REACTION ZONE WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS MATERIAL IS CONTINUOUSLY DEPOSITED ON THE COKE PARTICLES, REMOVING PROUCT VAPORS FROM THE COKING ZONE, HEATING A PORTION OF THE COKE PARTICLES FROM THE COKING ZONE IN A HEATING ZONE TO INCREASE THE TEMPERATURE OF SAID FLUIDIZED PARICLES, RETURNING A PORTION OF THE HEATED COKE PARTICLES FROM THE HEATING ZONE TO THE COKING ZONE AND WITHDRAWING COKE PRODUCT PARICLES, WHICH COMPRISES THE STEPS OF HEATING THE COKE PARTICLES WHILE IN THE FORM OF A HIGH VELOCITY DISPERSED SUSPENSION IN A TRANSFER LINE HEATING ZONE TO A TEMPERATURE IN THE RANGE OF ABOUT 2400*F. TO 3000*F. BY THE COMBUSTION INITIALLY OF AN ADDED GASEOUS EXTRANEOUS FUEL WITH AN OXYGEN-CONTAINING GAS, THE GASEOUS FUEL BEING UTILIZED IN AN AMOUNT OF ABOUT 0.5 TO 1.5 S.C.F./LB OF COKE SOLIDS AND OXYGEN-CONTAINING GAS BEING UTILIZED IN AN AMOUNT SO AS TO GIVE 10 TO 30 WT. PERCENT EXCESS OXYGEN ON COKE AFTER COMBUSTION OF THE GASEOUS EXTRANEOUS FUEL, THE COKE SOLIDS RESIDENCE TIME IN THE TRANSFER LINE HEATING ZONE BEING IN THE RANGE OF ABOUT 0.1 TO 3.0 SECONDS, SEPARATING THE THUS HEATED COKE PARTICLES FROM THE RESULTANT FLUE GAS, MAINTAINING THE COKE PARTICLES IN A SOAKING ZONE AT A TEMPERATURE IN THE RANGE OF ABOUT 2400*F. TO 3000*F. FOR A TIME INTERVAL OF ABOUT 0.5 TO 3 HOURS AND THEN WITHDRAWING THE DESULFURIZED COKE PARTICLES FROM THE SOAKING ZONE. 